1. Field of the Invention
The invention relates to a controller/driver for enabling a power MOSFET to be used for active ORing in redundant power systems. It relates more particularly to a controller/driver having a diagnostic feature for actively testing the condition of the power MOSFET.
2. Related Art
Power system redundancy is traditionally accomplished by combining two or more power sources into one redundant bus using diodes (commonly known as ORing diodes). ORing diodes are necessary to keep the common bus voltage present in case one of the OR-ed power sources fails short.
There are several typical applications of diode ORing. One is ORing of feed A and feed B sources in −48V carrier-class telecom systems, as shown in FIG. 1. Two input sources A and B are connected together through two diodes, which are connected to the negative sides of the sources. Another is ORing of N+1 redundant AC-DC rectifiers, which generate 48V or 24V to power various networking, telecom, high-end computing, or storage equipment. Lastly, high current low voltage outputs are often ORed together to provide redundant power for networking and computing processors.
When output power is low, diode ORing is a simple and low cost solution that provides quick and effective fault isolation. However, the best Schottky diodes on the market today used as ORing diodes often result in excessive power dissipation with high output power, requiring use of large packages and/or heat sinks. For example, the power level per system board in the proposed Advanced TCA spec is 200 W. The power dissipation due to diode ORing in this case can be as much as 3 W, or 1.5% of efficiency loss (for a standard 100V Schottky diode) at the worst-case input voltage (40.5V). Another problem with diode ORing is that it is not simple to detect potential diode short-circuit failure, which could result in loss of power redundancy.